The invention is directed towards controlled polymerization processes for monomers bearing ionic substituents and for preparation of block copolymers, including water soluble block copolymers. More specifically, the invention is directed towards extending and improving the utility of controlled or living radical (co)polymerization processes by disclosing the parameters and requirements for the controlled polymerization of radically (co)polymerizable monomers from initiators bearing additional functionality and provides for the direct production of polymers bearing ionic substituents by the direct (co)polymerization of monomers comprising ionic substituents, particularly in the presence of water.
There is a continuing effort in polymer chemistry to develop new polymerization processes and new polymers. A relatively recent development in polymer chemistry has been the development of controlled or living polymerization processes. A controlled or living polymerization process is one in which chain transfer and termination reaction are essentially nonexistent relative to the polymer propagation reaction. These developments have led to the production of polymers that exhibit macro functionality and to the development of functional polymers that possess specific chemical reactivity. The new polymers extend the level of control available to materials engineers in processing polymers and using polymers as building blocks in, or components for, subsequent material forming reactions, such as copolymerizations, chain extensions and crosslinking reactions, and interaction with substrates, including dispersed solids.
A significant economic hurdle which continually needs to be overcome in this effort is to provide the benefits of controlled polymerization from available low cost monomers in available commercial process equipment. These long term objectives have provided the backdrop, or driving force, for the continuing advances in controlled polymerization of radically (co)polymerizable monomers, disclosed in earlier patent applications, and provide the incentive to extend, simplify and make more robust the process known as atom transfer radical polymerization (ATRPo).
The recently developed ATRP process and polymers developed from the classic ATRP reaction are described in U.S. patent application Ser. No. 09/018,554, now U.S. Pat. No. 6,538,091 and 09/534,827, the entire contents of which are hereby incorporated herein by reference. Methods for exercising control over many parameters in a catalytic process for the controlled polymerization of a wide range of free radically (co)polymerizable monomers have been described in publications authored or co-authored by Krzysztof Matyjaszewski and others. See for example, Wang, J. S. and Matyjaszewsk, K., J. Am. Chem. Soc., vol. 117, p.5614 (1995); Wang, J. S. and Matyjaszewsk, K., Macromolecules, vol. 28, p. 7901 (1995); K. Matyjaszewski et al., Science, vol. 272, p.866 (1996); K. Matyjaszewski et al., xe2x80x9cZerovalent Metals in Controlled/xe2x80x9dlivingxe2x80x9d Radical Polymerization,xe2x80x9d Macromolecules, vol. 30, pp. 7348-7350 (1997); J. Xia and K. Matyjaszewski, xe2x80x9cControlled/xe2x80x9cLivingxe2x80x9d Radical Polymerization. Homogenous Reverse Atom Transfer Radical Polymerization Using AIBN as the Initiator,xe2x80x9d Macromolecules, vol. 30, pp. 7692-7696 (1997); U.S. patent application Ser. No. 09/126,768, now U.S. Pat. No. 6,121,371, the entire contents of which are hereby incorporated by reference; U.S. Pat. Nos. 5,807,937, 5,789,487, 5,910,549, 5,763,548, 5,789,489, 5,945,491, 6,111,022, 6,121,371, 6,124,411 and 6,162,882, and U.S. patent application Ser. No. 09/034,187, U.S. Pat. No. 6,407,187, Ser. No. 09/018,554, U.S. Pat. No. 6,538,091, Ser. No. 09/431,871, U.S. Pat. No. 6,162,882, Ser. Nos. 09/359,359, 09/359,591, U.S. Pat. No. 6,512,060, Ser. No. 09/369,157, U.S. Pat. No. 6,541,580, Ser. No. 09/126,768, U.S. Pat. No. 6,121,371, and Ser. No. 09/534,827, the entire contents of each are hereby incorporated herein by reference. The subtle interactions between the parameters have been further explored and implementation of the teachings disclosed in these publications has allowed the preparation of many inherently useful novel materials displaying control over functionality and topology, and production of novel tele-functional building blocks for further material forming reactions, resulting from application of the site specific functional and topological control attainable through this robust controlled polymerization process for free radically (co)polymerizable monomers.
The system or process employed to gain control over the polymerization of free radically (co)polymerizable monomers has been described in earlier applications as comprising the use of four components: (i) an initiator molecule; (ii) a transition metal compound having (iii) an added or associated counterion and the transition metal compound complexed with (iv) a ligand(s). The initiator molecule, or polymerization originator molecule may be any molecule comprising one or more radically transferable atom(s) or group(s) capable of participating in a reversible redox reaction with the transition metal compound. The transition metal compound may include an added or associated counterion and comprise a transition metal salt. So that all reactive oxidation states are soluble to some extent in the reaction medium, the transition metal may be complexed with the ligand(s). The components of the system may be optimized to provide more precise control for the (co)polymerization of the free radically polymerizable monomers. See U.S. Pat. No. 5,763,548, the entire contents of which are hereby incorporated herein by reference.
In an embodiment known as xe2x80x9creversexe2x80x9d ATRP, the initiator molecule described above can be formed in-situ by reaction of a free radical with the redox conjugate of the transition metal compound. Other components of the polymerization system such as the choice of the radically transferable atom or group, counterion initially present on the transition metal, and optional solvent may influence the process. U.S. Pat. No. 5,807,937 provides as an example of a single molecule containing a combination of functions, a complex in which the counterion and ligand components are in one molecule. The role of a deactivator, the xe2x80x9cpersistent radical,xe2x80x9d or for ATRP, the transition metal redox conjugate, is also described in U.S. Pat. No. 5,807,937.
While not to be limited to the following description, the theory behind ATRP disclosed in the previous work is that polymerization proceeds essentially by cleavage (and preferably essentially homolytic cleavage) of the radically transferable atom or group from the initiator molecule or, during the polymerization process the dormant polymer chain end, by a reversible redox reaction with a complexed transition metal catalyst, without any strong carbon-transition (C-Mt) bond formation between the active growing polymer chain end and the transition metal complex. Within this theory as the transition metal complex, in a lower active oxidation state, or in its activator state, activates the initiator or dormant polymer chain end by homolytically removing the radically transferable atom or group from the initiating molecule, or growing polymer chain end, in a reversible redox reaction, an active species is formed that allows other chemistry, essentially free radical based chemistry to be conducted. The transition metal complex in the higher oxidation state, the redox conjugate state or deactivator state, transfers a radically transferable atom or group to the active initiator molecule or growing chain end, thereby reforming the lower oxidation state transition metal complex. When free radical based chemistry occurs, a new molecule comprising a radically transferable atom or group is also formed. In prior publications, the catalytically active transition metal compound, which can be formed in situ or added as a preformed complex, has been described as containing a range of counterions. The counterion(s) may be the same as the radically transferable atom or group present on the initiator, for example a halide such as chlorine or bromine, or may be different radically transferable atoms or groups. An example of the latter counterion is a chloride counterion on the transition metal compound when the initiator first contains a bromine. Such a combination allows for efficient initiation of the polymerization followed by a controlled rate of polymerization, and has additionally been shown to be useful in certain crossover reactions, from one set of (co)monomers to a second set of (co)monomers, allowing efficient formation of block copolymers.
For the present purposes xe2x80x9cpolymersxe2x80x9d include homopolymers and copolymers (unless the specific context indicates otherwise), which may be block, random, statistical periodic, gradient star, graft, comb, (hyper)branched or dendritic polymers. The xe2x80x9c(co)xe2x80x9d parenthetical prefix in conventional terminology is an alternative, viz., xe2x80x9c(co)polymer means a copolymer or polymer, including homopolymer, while xe2x80x9c(co)polymerizable means a monomer that is directly polymerized by the polymerization mechanism being discussed and additionally includes a comonomer which can only be incorporated into the polymer by copolymerization. Similarly xe2x80x9c(hyper)xe2x80x9d is meant to incorporate the concept that the degree of branching along the polymer backbone can vary from a low degree of branching up to a very high degree of branching.
Here, and elsewhere in the text the word xe2x80x9ccontrol and/or controlledxe2x80x9d means that in the polymerization process conditions are defined whereby the contributions of the chain breaking processes are insignificant compared to chain propagation, so that polymers with predetermined molecular weights, low polydispersities and high functionalities are achievable.
It is widely accepted that controlled polymerization should display the following features.
Feature 1.
First-order kinetics behavior, i.e. the polymerization rate (Rp) with respect to the monomer concentration ([M]) is a linear function of time. This is due to the lack of termination, so that the concentration of the active propagating species ([P*]) is constant.                               R          p                =                                            -                              ⅆ                                  [                  M                  ]                                                                    ⅆ              t                                =                                                    k                p                            ⁡                              [                                  P                  *                                ]                                      ⁡                          [              M              ]                                                          (        1.1        )                                          ln          ⁢                                                    [                M                ]                            0                                      [              M              ]                                      =                                                            k                p                            ⁡                              [                                  P                  *                                ]                                      ⁢            t                    =                                                    k                p                app                            [                              P                *                            }                        ⁢            t            ⁢                          xe2x80x83                        ⁢                          (                                                if                  ⁢                                      xe2x80x83                                    [                                      P                    *                                    ]                                ⁢                                  xe2x80x83                                ⁢                is                ⁢                                  xe2x80x83                                ⁢                constant                            )                                                          (        1.2        )            
kp is the propagation constant. The result of eq.1.2 is illustrated in FIG. 1.
FIG. 1 is a semilogarithmic plot and is very sensitive to the change of the concentration of the active propagating species. A constant [P*] is revealed by a straight line, and an upward curvature indicates an increased [P*], which occurs in case of a slow initiation. On the other hand, a downward curvature suggests the decrease of [P*], which may result from termination or some other side reactions such as the catalytic system being poisoned.
It should also be noted that the semilogarithmic plot is not sensitive to chain transfer process or slow exchange between different active species, since they do not affect the number of the active propagating species.
Feature 2.
Predetermined degree of polymerization (Xn), i.e. the number average molecular weight (Mn) is a linear function of monomer conversion.                               X          n                =                                            M              n                                      M              0                                =                                                    Δ                ⁡                                  [                  M                  ]                                                                              [                  I                  ]                                0                                      =                                                                                [                    M                    ]                                    0                                                                      [                    I                    ]                                    0                                            ⁢                              xe2x80x83                            ⁢                              (                conversion                )                                                                        (        1.3        )            
This result comes from a constant number of chains throughout the polymerization, which requires the following two conditions:
the initiation should be sufficiently fast so that nearly all chains start to grow simultaneously;
no chain transfer occurs to increase the total number of chains. FIG. 2 illustrates the ideal growth of molecular weights with conversion, as well as the effects of slow initiation and chain transfer on the molecular weight evolution.
Importantly, the evolution of molecular weights is not very sensitive to chain termination, since the number of chains remains unchanged. Only when coupling reaction plays a significant role for polymers with very high molecular weights, is the effect of termination observable on the plot.
Feature 3.
Narrow molecular weight distribution. Although this feature is very desirable, it is not necessarily the result from a controlled polymerization, which requires only the absence of chain transfer and termination, but ignores the rate of initiation, exchange and depropagation. Substantial studies [Gold, 1958 #84; Coleman, 1963 #88; Matyjaszewski, 1995 #85; Hsieh, 1996 #81; Matyjaszewski, 1996 #86] indicate that in order to obtain a polymer with a narrow molecular weight distribution, each of the following five requirements should be fulfilled.
i. The rate of initiation is competitive with the rate of propagation. This condition allows the simultaneous growth of all the polymer chain.
ii. The exchange between species of different reactivities is faster than propagation. This condition ensures that all the active chain termini are equally susceptible to reaction with monomer for a uniform growth.
iii. There must be negligible chain transfer or termination.
iv. The rate of depropagation is substantially lower than propagation. This guarantees that the polymerization is irreversible.
v. The system is homogenous and mixing is sufficiently fast. Therefore all active centers are introduced at the onset of the polymerization.
This should yield a Poison distribution, as quantified in eq.1.4.                                           X            w                                X            n                          =                                            M              w                                      M              n                                =                                    1              +                                                X                  n                                                                      (                                                                  X                        n                                            +                      1                                        )                                    2                                                      ≅                          1              +                              1                                  X                  n                                                                                        (        1.4        )            
According to eq.1.4, polydispersity (Mw/Mn) decreases with increasing molecular weight. A polymerization that satisfies all five prerequisites listed above is expected to have a final polymer with a polydispersity less than 1.1 for Xn greater than 10.
Feature 4.
Long-lived polymer chains. This is a consequence of the negligible chain transfer and termination. Hence, all the chains retain their active centers after the full consumption of the monomer. Propagation resumes upon the introduction of additional monomer. This unique feature enables the preparation of block copolymers by sequential monomer addition.
The significance of controlled polymerization as a synthetic tool is widely recognized. Polymers having uniform and predictable chain length are readily available. Controlled polymerization provides the best opportunity to control the bulk properties by selection and control of various aspects of the multitude of variations in composition, functionality and topology at a molecular level. The result of such control over the preparation of polymeric materials is shown schematically in FIG. 3.
ATRP is one of the most promising methods in the field of controlled/xe2x80x9clivingxe2x80x9d radical polymerizations, one which can be applied to a wide variety of monomers and provide well defined polymers. However, only a very limited range of polar, water soluble or hydrophilic monomers could be polymerized by ATRP processes particularly in aqueous systems. Monomers comprising a polar, or an ionic substituant, can be very efficient complexing agents for one or more of the oxidation states of the transition metal catalyst as it participates in the repetitive redox reaction with the initiator or growing polymer chain and this was thought to be a limitation on the range of monomers that could be used as comonomers in ATRP. However, since polymers with a full range of in-chain, or terminal ionic functionality, find application in the preparation of composite structures, adhesives, and in coating products in addition to personal care products by offering a means to control interfacial chemistry there was an incentive to overcome this limitation and directly prepare materials incorporating monomers with disparate functionality into copolymers. ATRP reactions are complicated by the interactions of the components of the reaction medium, for instance, monomer may interact with the transition metal catalyst, the solvent may interact with the monomer and the solvent may interact with the initiator. Thus there exists a need for a process for polymerizing polar and ionic monomers by ATRP and a need for the novel polymers which may be prepared by such a process. Further, there is a need for a process for the controlled polymerization of water soluble macroinitiators.
The present invention provides a controlled polymerization process for initiating the polymerization of free radically (co)polymerizable polar or ionic monomers in the presence of a system initially including a transition metal complex, and an initiator comprising a radically transferable azide group particularly in aqueous systems. Additionally, a controlled polymerization process for (co)polymerization of radically polymerizable ionic monomer including initiating the polymerization of free radically (co)polymerizable ionic monomers in the presence of a system initially comprising a transition metal complex, and an initiator comprising a radically transferable atom or group, and an excess of one or more uncomplexed ligands is provided. The uncomplexed ligands stabilize the transition metal complex and reduce the disproportionation of the transition metal. Ionic monomers polymerizable by this process include both anionic and cationic monomers.
A controlled polymerization process for the preparation of water soluble block copolymers including the use of water soluble macroinitiators is also provided in the present invention. As well as novel polymers consisting of water soluble blocks that have not been previously prepared prior to the present invention.
Additionally, the present invention includes procedures for synthesis of novel water soluble block copolymers, block copolymers comprising monomers with polar functionality, block copolymers with monomers comprising ionic functionality and zwitterionic block copolymers in homogeneous aqueous systems.